Ink sheet

Abstract: A color thermal printer using an ink sheet (4) having a set of three or four colorants (4b-e) coated or printed so as to correspond to a print area with sensor marks (4g) arranged at boundaries between the colorants. In the color thermal printer, a plurality of sensors are disposed within a print width of a thermal head and downstream from a heat line of the thermal head in an ink sheet forward direction by a predetermined distance. When the sensors have sensed the sensor marks, the ink sheet is rewound by the predetermined distance to cause the printing operation to be effected.

Description: BACKGROUND OF THE INVENTION The invention relates to an ink sheet as defined in the preamble of claim 1. Figure 13 is a diagram showing a main portion of a construction of a conventional color thermal printer disclosed in JP-A-64 005 879, while Figure 14 is a diagram showing a conventional ink sheet. In Figures 13 and 14, reference numeral 1 designates a platen; 2, a thermal head mounted on a radiating plate 2a and having a linearly formed heating body; 3, a print sheet; and 4, a conventional ink sheet. The ink sheet 4 is prepared by coating or printing three (3) colorants, namely, yellow (Y) 4b, magenta (M) 4c, cyan (C) 4d, on a base film 4a in succession so as to correspond respectively to a print area. An ink sheet having four (4) colorants including black (BK) 4e is also available. A head color mark 4f for allowing the head color of each set to be sensed and an identification mark (ID mark) 4g for aligning each color with a print start position and for identifying the type of ink sheet are arranged. The head color mark 4f and the ID mark 4g are sensor marks. The head color mark 4f and the ID mark 4g, which are sensor marks, are coated with a highly light-shielding paint. Reference numeral 5 designates an ink sheet feed roll; 6, an ink sheet take-up roll; and 7, a sensor for sensing light-shielding at the sensor marks. An operation of the printer will be described next. Almost simultaneously with the print sheet 3 having been forwarded to the print start position, the conventional ink sheet 4 is also forwarded toward the ink sheet take-up roll 6 from the ink sheet feed roll 5. At this instance, the head color mark 4f is sensed by the sensor 7 and the forwarding of the ink sheet 4 is thus stopped. The platen 1 is rotated at a predetermined speed by applying an electric signal corresponding to an image to the thermal head 2 with the print sheet 3 and the ink sheet 4 interposed between the platen 1 and the thermal head 2, and under this condition, the colorant, yellow 4b, is thermally transferred onto the print sheet 3 first. Then, the thermal head 2 is moved away from the platen 1 and the print sheet 3 is returned to the print start position, and at the same time, the ink sheet 4 is forwarded to the next color. The forwarding of the ink sheet 4 is stopped when the ID mark 4g has been sensed by the sensor 7 in the course of forwarding, and the thermal head 2 is caused to abut against the platen 1 to start printing the next colorant (magenta 4c) on the print sheet 3. The colorants, cyan 4d and black 4e, are similarly thermally transferred to complete the printing. The conventional color thermal printer and the conventional ink sheet are constructed as described above. The sensor 7 is disposed within a print width of the thermal head 2 since the head color marks 4f and the ID marks 4g are arranged at the boundaries between the colorants. While it is desirable to make the distance between the heat line of the thermal head 2 and the sensor 7 as short as possible, a distance L is by all means required since the radiating plate 2a and a guide roller (no reference numeral is designated) are present on the way. As a result, the distance L from the head color mark 4f or the ID mark 4g sensed by the sensor 7 to a colorant to be used for printing becomes a wasteful portion on the ink sheet 4, thus making the outer diameters of the ink sheet feed roll 5 and the ink sheet take-up roll 6 large. Figure 15 is a diagram showing the relationship between a conventional ink sheet and the sensor in another conventional example disclosed in JP-A-64 005 879, on which the preamble of claim 1 is based. In Figure 15, reference characters 4 and 4a to 4g designate the same parts and components as those described above. Since the head color mark 4f and the ID mark 4g are arranged out of the print width of the thermal head 2 in the second conventional example, the print start position can be close to the boundary of each colorant by interposing only a distance L between the sensor 7 and the boundary of each colorant, thus producing no such waste as the distance L in the first conventional example. However, since the sensor 7 is disposed outside the print width of the thermal head 2, the ink sheet 4 must include such margins as to allow the head color marks 4f and the ID marks 4g to be therein arranged in addition to a width W1 of the colorant, which makes the width of the ink sheet 4 as wide as W2 (W1 < W2). Document EP-A-0 561 347 discloses a conventional ink sheet which is similar to the above-mentioned ink sheet according to figure 15. In detail, this conventional ink sheet is divided into a plurality of sets of three or four colorants, i.e. yellow, magenta, cyan and black. At the boundary of each colorant color identification marks are provided for the identification of the respective color and for aligning each color with a print start position. In addition, at the boundary of each set of colorants, there are provided head color marks which indicate a head color of each set of colorants. However, similar to the conventional ink sheet according to figure 15 or figure 14, the pattern of the color identification marks and the head color marks differs from each other, which results in a complex manufacturing process. Finally, document US-A-5,037,218 discloses a further conventional ink sheet used in a thermal transfer printer. However, this conventional ink sheet does not make use of color identification marks for identifying the position of each colorant, but discloses in some embodiments a kind of "head color marks" indicating a position of each set of colorants and giving information of the color sequence of the following color regions on the ink sheet for printing. Consequently, a position of the respective colorants is derived from a transport length of the ink sheet. It therefore is an object of the present invention to provide an ink sheet for accurate printing which can be produced in a simple manner and at low costs. According to the present invention this object is achieved by the measures indicated in present independent claim 1. BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the objects, advantages and principles of the invention. In the drawings, Figure 1 is a diagram showing a main portion of a construction of a color thermal printer used for the present invention; Figure 2 is a diagram showing an ink sheet not forming part of the present invention; Figure 3 is a flowchart illustrative of an operation of the printer according to Fig. 1; Figure 4 is a diagram showing a relationship between an ink sheet and sensors of a first embodiment of the present invention; Figure 5 is a diagram showing a truth table of the light-shielding characteristics by the ink colorant and the type of sensor; Figure 6 is a graph showing spectral characteristics of colorants of an ink sheet; Figure 7 is a flowchart illustrative of an operation of the printer using the ink sheet according to Fig. 4; Figure 8 is a diagram showing a main portion of a construction of a further color thermal printer used for the present invention; Figure 9 is a diagram showing a relationship between an ink sheet and a red light sensor of a second embodiment of the present invention; Figure 10 is a flowchart illustrative of an operation of the printer using the ink sheet according to Fig. 9; Figure 11 is a diagram showing a relationship between the ink sheet and the sensing of the red light sensor of a third embodiment of the present invention; Figure 12 is a flowchart illustrative of an operation of the printer using the ink sheet according to Fig. 11; Figure 13 is a diagram showing a main portion of a construction of a conventional color thermal printer; Figure 14 is a diagram of a conventional ink sheet; and Figure 15 is a diagram of another conventional ink sheet. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Figure 1 is a diagram showing a main portion of a construction of a color thermal printer used for the present invention; and Figure 2 is a diagram of an ink sheet not forming part of the present invention. In Figures 1 and 2, reference characters 1 to 6 and 4a to 4g designate the same parts and components of the conventional examples. In this example, such an ink sheet as having a head color mark 4f and an identification mark (ID mark) 4g that identifies the division of colors at a boundary between colors is used. The ID mark 4g has a recognition pattern that is formed of a combination of a plurality of light-shielding portions and light-transmitting portions so that not only the head of each color can be sensed but also the type of ink sheet (three colors, four colors, print area size, sublimated ink, molten ink, or the like) can be identified simultaneously. The ID marks 4g of the same pattern are arranged at the boundaries between colors within a roll of ink sheet. Generally, the boundaries separate colorants from one another by leaving transparent portions on a base film 4a with no colorants coated for a predetermined width to prevent mixture of the colorants. Each ID mark 4g is therefore arranged on a part of the transparent portion. Reference numeral 8 designates a sensor block in which a plurality of sensors are arranged in a row. The row of sensors is arranged in substantially parallel with a heating body line of a thermal head 2 that is downstream in the printing process. The thermal head 2 and the sensing point of the sensor block 8 are apart from each other by a distance L. Reference numeral 9 designates a control section, which controls not only rotation of a platen 1 and printing by the thermal head 2, but also drive motors (not shown) of an ink sheet feed roll 5 and an ink sheet take-up roll 6 in response to recognition signals from sensors of the sensor block 8 in this example. An operation of this example will be described with reference to a control flow shown in Figure 3. A print sheet 3 is fed to a print start position by an image print start command (Step 101). Almost simultaneously therewith, an ink sheet 4 is also forwarded up to a position where the sensors of the sensor block 8 sense an ID mark 4g and stopped thereat (Steps 102 and 103). A type of ink sheet 4 on which to effect printing is judged from the ID mark 4g, and a print execution sequence, a control parameter and the like are then selected (Step 104). If a head color mark 4f is sensed simultaneously therewith, a next step is executed. if not, the ink sheet 4 is forwarded until a head color mark 4f is sensed (Step 105). Since the sensor block 8 for sensing the head color mark 4f or the ID mark 4g is apart from the heating body line of the thermal head 2 by the distance L, the ink sheet 4 is rewound by the distance L (Step 106) so that the head of a colorant, yellow 4b, coincides with the heating body position of the thermal head 2 to thereby execute printing (Steps 107 and 108). When printing of the first color (yellow) has been ended, the print sheet 3 is moved to the print start position, and the ink sheet 4 is forwarded (Steps 109 to 113). When the ID mark 4g of a next color has been sensed by the sensors of the sensor block 8 (Step 114), the forwarding operation is stopped. The ink sheet 4 is then rewound by the distance L (Step 106), and printing of the second color (magenta) is effected. In a similar manner, the third color (cyan) and the fourth color (black) are printed to complete the printing operation. Since the first example is designed as described above, there is no wasteful distance L between the thermal head 2 and the sensing point of the sensor block 8 at each colorant-coated portion on the ink sheet 4, thereby contributing to decreasing the ink sheet roll diameter. Figure 4 is a diagram showing the relationship between an ink sheet and the sensors of a first embodiment of the present invention; Figure 5 is a diagram showing a truth table of light-shielding characteristics by the types of ink colorants and sensors; Figure 6 is a graph showing spectral characteristics of the respective colorants on the ink sheet, in which the transmittance is indicated in function of the wavelength of each color with the axis of ordinate showing the transmittance, and the axis of abscissa showing the wavelength of light; and Figure 7 is a flowchart illustrative of a control flow of an operation of the second embodiment. In Figures 4 to 7, reference characters 4, 4a to 4e, 4g, and 8 designate the same parts and components as those of the example. At the boundaries of the respective colorants on the ink sheet 4 are ID marks 4g; there, are no head color marks. Reference character 8a designates a red light sensor; 8b, green light sensor; and 8c, an infrared light sensor. As shown in Figure 6, the light-shielding rate of the red light sensor 8a is high for cyan and black, but low for yellow and magenta. The light-shielding rate of the green light sensor 8b is high for magenta and black, but low for yellow and cyan. The infrared light sensor 8c does not shield light at portions other than the sensor marks. This relationship can be expressed in a truth table shown in Figure 5. When both the red light sensor 8a and the green light sensor 8b receive a light-transmitting signal, the head color, which is yellow, is able to be detected. Since the light of the red light sensor 8a and that of the green light sensor 8b are shielded by a sensor mark at a boundary between colorants and the light is naturally transmitted by a transparent portion where no sensor mark is coated, the combination of such sensing results can be shared as the identification bits of the ID mark 4g. An operation control flow of the printer using the ink sheet according to the first embodiment of the invention will be described with reference to Figure 7. The same functions as in the example are designated by the same step numbers as those of Figure 3. Since the steps from the print sheet feed operation (Step 101) to the ink sheet type judging operation (Step 104) are the same as those of the example, descriptions thereof will be omitted. Upon sensing of an ID mark 4g at the sensor block 8 position, the ink sheet 4 is further forwarded by a second predetermined distance L2 (Step 201) and the signals of the red light sensor 8a and the green light sensor 8b are checked. If either the red light sensor 8a or the green light sensor 8b outputs a light-shielding signal, then the colorant right below the sensor block 8 is judged to be a colorant other than yellow, so that the same operation is repeated until the head color, yellow, is sensed. When both light sensors 8a and 8b output light-transmitting signals, the head color, yellow, is sensed (Steps 202 and 203). When the colorant right below the sensor block 8 has been sensed as yellow, the ink sheet 4 is rewound by a third predetermined distance L3 = L + L2 (Step 204) to cause the head of the colorant, yellow 4b, to coincide with the position of the heating body of the thermal head 2 and to effect printing (Steps 107 and 108). Since the subsequent steps are the same as those of the example, descriptions thereof will be omitted. As a result of the above construction and control operation, a sensor dedicated to reading the head color mark 4f can be dispensed with. This makes it unnecessary to increase the number of sensors even if the number of ink sheet types is increased to thereby increase the number of recognition bits used for the ID mark 4g. Further, the head color mark 4f is no longer necessary for the ink sheet of the present invention, which leaves only the ID mark of a single pattern as the sensor mark arranged at every boundary between colorants, thereby contributing to simplifying the ink sheet manufacturing process. While the red light sensor 8a and the green light sensor 8b are used to sense the head color (yellow) in the first embodiment, a second embodiment of the invention is designed to sense the head color (yellow) only by the red light sensor 8a. Figure 8 is a diagram showing a main portion of a construction of a further color thermal printer used for the present invention; Figure 9 is a diagram showing the relationship between the ink sheet and the sensing of the red light sensor of a second embodiment; and Figure 10 is a flowchart illustrative of a operation control flow of the printer using the ink sheet of the second embodiment. In Figures 8 to 10, reference characters 1 to 9, 4a to 4e, and 4g designate the same parts and components as those of the example; and 10 and 11, a first memory and a second memory connected to a control section 9. An operation control flow of the second embodiment of the invention will be described with reference to Figure 10. The ink sheet 4 is forwarded in a manner similar to that in the first embodiment, and the same functions are designated by the same step numbers as those of Figure 7. The steps from the print sheet feed operation (Step 101) to the operation of forwarding the ink sheet 4 by the second predetermined distance L2 (Step 201) are the same as those of the first embodiment, so that descriptions thereof will be omitted. The sensing result obtained by the red light sensor 8a at this position is stored in the first memory 10 (Step 301). The ink sheet 4 is then rewound by the third predetermined distance L3 = L + L2 (Step 204). This is not only a position at which the head of a colorant on the ink sheet 4 coincides with the heating body of the thermal head 2, but also a position at which the red light sensor 8a of the sensor block 8 senses a colorant just before such colorant. The sensing result obtained by the red light sensor 8a at this position is stored in the second memory 11 (Step 302). If the first memory 10 stores "0" and the second memory 11 stores "1" ("0" means that light is transmitted, and "1" means that light is shielded), then the colorant on the ink sheet 4 at the heating body line of the thermal head 2 is judged yellow 4b. The reason therefor will now be described. Colorants transmitting light of the red light sensor 8a are yellow 4b and magenta 4c, whereas the colorants shielding the light are cyan 4d and black 4e. The only combination that satisfies a requirement that the light be transmitted at the timing of storage in the first memory 10 and is shielded at the timing of storage in the second memory 11 is a combination of yellow 4b and black 4e for a four-color ink sheet. Also, the only combination that satisfies the same requirement for a three-color ink sheet is a combination of yellow 4b and cyan 4d. Therefore, the colorant, yellow 4b, can be sensed by selecting this condition. As a result of the above construction, the second embodiment of the invention can judge yellow, which is the head color, only by a single sensor, the red light sensor 8a. In the example, it has been described that portions having no coating of colorant are arranged for a predetermined width to prevent mixture of colorants at the boundaries. This design is implemented for ink sheets with molten colorants. However, ink sheets of sublimated colorants, not exhibiting mixture of colorants, requires no interval between colorants, and therefore it is possible to fabricate ink sheets such as shown in Figure 11. Figure 11 is a diagram showing the relationship between the ink sheet and the sensing of the red light sensor of a third embodiment of the invention. A color thermal printer whose construction is the same in main portion as that of Figure 8 is used. In Figure 11, reference characters 4a to 4e, and 4g designate the same parts and components as those of the second embodiment. The ink sheet shown in Figure 11 has a coating or printing of sublimated colorants, and there are no transparent portions at the boundaries between colorants. Each ID mark 4g is coated or printed so as to be superposed on each colorant at the head of the colorant. Figure 12 is a flowchart illustrative of an operation control flow of the printer using the ink sheet of the third embodiment. The same functions are designated by the same step numbers as those of Figure 10. The steps from the print sheet feed operation (Step 101) to the ink sheet 4 type judging operation (Step 104) are the same as those of the second embodiment, so that descriptions thereof will be omitted. As described above, the type of the ink sheet 4 is judged (Step 104) and the colorant sensing result obtained by the red light sensor 8a is stored in the first memory 10 (Step 301) simultaneously. Then, the ink sheet 4 is rewound by the predetermined distance L (Step 106) to cause the head of the colorant to coincide with the heating body line of the thermal head 2, and a sensing result obtained by the red light sensor 8a that has sensed a colorant at the sensor block 8 downstream from this position by the predetermined distance L is stored in the second memory 11 (Step 302). If a condition that the first memory 10 has "0", meaning that the colorant has transmitted the light and that the second memory 11 has "1", meaning that the colorant has shielded the light is satisfied (Step 303), the head colorant, yellow, is selected, which allows the printing operation to be started. When the ink sheet of the third embodiment is used, the reading of an ID mark 4g and the sensing of light-shielding and light-transmission of a colorant using the red light sensor 8a can be effected at the same position, thereby making the forwarding of the ink sheet by the second predetermined distance L2 unnecessary and thereby allowing the operation to be simplified. While the example and the first to second embodiments are applicable to both molten and sublimated ink sheets, the third embodiment is applicable only to sublimated ink sheets because of their ink sheet manufacturing restrictions. The color thermal printer according to the example is designed to rewind the ink sheet by a predetermined distance when the sensors have sensed a sensor mark and to start printing. Therefore, waste of the ink sheet for the predetermined distance between the heating body line of the thermal head and the sensors can be dispensed with, which in turn eliminates waste of the distance L between the thermal head of the ink sheet and the sensor block. As a result, the ink sheet roll diameter can be reduced, which contributes to downsizing the printer. The color thermal printer used for the ink sheet according to the first embodiment of the invention is designed to sense a head colorant out of a set of colorants at a position to which the ink sheet has reached while further forwarded by a second predetermined distance by selecting a predetermined condition of combination of sensing operations by two sensors, which are the green light sensor and the red light sensor. Therefore, the sensor dedicated to reading the ID mark can be dispensed with, which in turn contributes to not increasing the number of sensors even if the number of recognition bits of the ID mark is increased due to an increase in the number of types of ink sheets. In particular, no head mark is necessary for the ink sheet itself, which makes an ID mark only the sensor mark to be arranged at each boundary between colorants. As a result, the ink sheet fabricating process can be simplified. The color thermal printer used for the ink sheet according to the second embodiment of the present invention is designed to sense the head colorant by selecting a condition of combination of sensing results obtained by the red light sensor at the position to which the ink sheet has reached while forwarded by the second predetermined distance and at the position to which the ink sheet has reached while rewound by the third predetermined distance, the red light sensor being capable of sensing the yellow colorant as well as the cyan and the black colorants. Therefore, yellow can be judged by the only one sensor, the red light sensor. The color thermal printer used for the ink sheet according to the third embodiment of the present invention is designed so that a sensor mark is superposed on a part of a colorant on the ink sheet. Therefore, the ID mark can be sensed by the red light sensor at the same position as that at which the colorant shields or transmits light. This dispenses with the forwarding of the ink sheet by the second predetermined distance L2, and therefore, makes the operation simple.

Claims: An ink sheet (4) for thermal printing having a plurality of sets of three or four colorants (4b, 4c, 4d, 4e) coated or printed thereon in succession so as to correspond respectively to a print area, wherein color identification marks for aligning each color with a print start position are arranged at boundaries between each said colorant (4b, 4c, 4d, 4e) and head color marks for indicating a head color of each set of colorants are arranged at boundaries between each said set of colorants characterized in that said marks have a pattern that is formed of a combination of light-shielding portions and light-transmitting portions and said color identification marks and said head color marks have the same pattern. The ink sheet according to claim 1, characterized in that a blank area (4a) in which no colorants are coated is arranged between the colorants (4b, 4c, 4d, 4e), and said color identification marks and said head color marks are arranged in the blank areas (4a) forming the boundaries between the colorants (4b, 4c, 4d, 4e). The ink sheet according to claim 1, characterized in that each of said color identification marks and said head color marks are arranged on at least one of the colorants (4b, 4c, 4d, 4e), said colorants (4b, 4c, 4d, 4e) being directly contiguous to each other. The ink sheet according to one of claims 1 through 3, characterized in that each of the color identification marks and said head color marks is to identify any of the number of the colorants, a print area size, and a type of an ink used, or combinations thereof.

Inventors: KITAMURA SYOZO, KOUZAI FUMIO, TOKUMARU SUSUMU, KITAMURA, SYOZO, KOUZAI, FUMIO, TOKUMARU, SUSUMU, KITAMURA, SYOZO, C/O MITSUBISHI DENKI K.K., KOUZAI, FUMIO, C/O MITSUBISHI DENKI K.K., TOKUMARU, SUSUMU, C/O MITSUBISHI DENKI K.K.
Applicants: MITSUBISHI ELECTRIC CORP, MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1994
Main classification: B41M5
IPC codes: B41M5, B41J35, B41J2